An overdraft occurs when a bank account holder withdraws more money than is available in their account, resulting in a negative balance. This can happen through checks, debit card transactions, or automatic payments. Banks may allow overdrafts as a courtesy, but they often charge fees for this service. When an account is overdrawn, the bank may cover the excess amount, but the account holder is responsible for repaying it. Some banks offer overdraft protection, which links a savings account or credit line to cover overdrafts, helping to avoid fees and declined transactions.